The nature of the interactions between flavin coenzymes and their apoproteins is being investigated using spectroscopic and kinetic methods. Temperature-jump and stopped-flow measurements of flavin analog binding to protein provide insight into the rate-determining processes and occurrence of protein conformational changes. Circular dichroism and fluorescence spectroscopy are also being used as indicators of protein changes. Chemical modification studies are being used to obtain information about protein side chains in the flavin binding site. The amino acid sequence of the Shethna flavoprotein from Azotobacter is being determined. BIBLIOGRAPHIC REFERENCES: G. Tollin and F. Rizzuto, "Rates of Oxidation and Disproportionation of Semiquinone Forms of Free Flavins and Flavodoxins", Proc. L. Michaelis Symp. Jap. Biochem. Soc., K. Yagi, Ed., 1975. K. Shiga, G. Tollin, M.C. Falk and D.B. McCormick, "Binding and Oxidation Reduction of Monoamine Oxidase-type 8 alpha (S-Peptidyl) Flavins with Azotobacter (Shethna) Flavodoxin", Biochem. Biophys. Res. Commun. 66, 227 (1975).